1. Field of the Invention
The present invention relates to a memory device and to a method of accessing a memory device, in particular to a memory device and to a method of accessing a memory device comprising a high-speed bus for accessing the memory.
2. Description and Related Art
A known memory system will be elucidated in more detail hereinafter by way of FIG. 1. The memory system in FIG. 1 comprises a memory module 100 having a plurality of memory elements 1021, 1022, . . . 102n. The memory elements are, for example, DRAM memory elements. The memory system comprises, furthermore, a bus system 104 having a plurality of partial busses 1061 . . . 106n, each of the partial busses having a predetermined bit width and being connected to an associated memory element, e.g. partial bus 1061 to memory element 1021, and partial bus 106n to memory element 102n. The ends of the bus system 104 remote from memory module 100 are connected to a control unit 108 which, depending on signals received, outputs commands to the bus system 104 so as to render possible accessing of the memory module 100, or rather the memory elements 1021 to 102n arranged in the memory module.
The memory system illustrated in FIG. 1 is a high-speed memory system operating at clock frequencies in the range from approx. 200 MHz. In particular, the memory system illustrated in FIG. 1 makes use of a high-speed memory bus system, and a problem of the arrangement illustrated in FIG. 1 arises, due to the high-speed application, in connection with the heat developing in the memory elements 102n. The cause of the heat development in the memory elements 1021 to 102n is to be seen for one thing in that the memory element is effective as source, with the power consumed in the memory element, e.g. the DRAM, increasing with increasing signal frequency. The power consumed can be calculated as follows:
PDram=Cxc3x97fxc3x97xcex94u2 
wherein:
C represents the capacitance of the control unit and the bus (1061-106n),
xcex94u represents the voltage level difference of the outer data signal, and
f represents the signal or clock frequency (outer bus clock frequency).
The above equation easily shows that the power consumed in the memory element will increase with increasing signal or clock frequency.
A second cause for the development of heat in the memory element arises when the memory element is effective as receiver only. For conventional non-high-speed applications, the receiver memory element acts as input capacitance only which, however, hardly makes itself felt in the power budget. This does not hold for high-speed systems, since in that case the receiver (memory element) is provided with a terminating impedance for terminating the bus, which considerably contributes in heating the memory element, since a dc component flows through the terminating impedance when the usual driver concepts (push-pull and open-drain) are employed.
In operation, the afore-mentioned causes in connection with the heating of the memory elements in conventional high-speed memory systems have the following effect. The conventional practice in a memory system consists in reading or writing all bits of the bus 104 simultaneously via the bus, i.e. the command xe2x80x9cREADxe2x80x9d or xe2x80x9cWRITExe2x80x9d is always applied simultaneously to the entire bus 104, as illustrated in FIG. 1 schematically for partial busses 1061 and 106n that each have a write command 110 arranged thereon. The thermal load on the memory element is, however, different depending on whether a data bit is read from the memory element or written into the same. In case of bus systems having a terminating impedance, reading of the memory element results in little power consumption only, whereas writing of bits into the memory element is accompanied by comparatively higher power consumption.
The disadvantage of the bus systems illustrated in FIG. 1 consists in that in such conventional arrangements a command always is given to the entire memory module, so that in case of a command, e.g. the write command, the module experiences uniform/uniformly distributed heating.
There are various approaches known in the prior art for avoiding heating of the memory module. It is known, for example, that memory components comprising individual memory modules have a metallic heat spreader associated therewith for improved dissipation of heat. The disadvantage of this approach consists in that the utilization of the heat spreader for the memory module renders possible heat dissipation/heat spreading only if there is a thermal gradient present across the memory module. However, as described hereinbefore, a memory module experiences uniform heating upon application of a command to the bus, i.e. there is no thermal gradient across the memory module, so that no heat spreader can be employed that only has the area of the memory module proper. The heat spreader thus cannot be utilized for heat dissipation/heat spreading in conventional memory modules.
It is the object of the present invention to provide an improved method of accessing a memory module as well as a memory device in which undesired heating of the memory module at high clock frequencies can be avoided.
The present invention is a method of accessing a memory module via a bus, in which, during an accessing operation, a first command that causes high power consumption in the memory module, is applied to the memory module via part of the bus only.
The present invention is a memory device having a memory module, a control unit and a bus connected to the memory module and the control unit, with the control unit, during accessing of the memory module, applying a first command that causes high power consumption in the memory module, to the memory module via part of the bus only.
The present invention is based on the realization that a heat spreader having the size of the module only may me employed if it is possible to generate a thermal gradient across the module associated with the heat spreader. According to the invention, this is achieved in that commands with high power consumption are applied to part of the bus only, which in turn results in stronger heating in the portion of the module receiving this command, whereas other portions of the module are not heated to such a high extent, so that the thermal gradient across the memory module is achieved that is necessary for utilization of the heat spreader.
The heat generated in the memory module during accessing is dissipated/spread by the memory module via the heat spreader.
According to a preferred embodiment of the present invention, the memory module comprises a plurality of memory elements, and the first command is applied to part of the memory elements.
According to a further embodiment of the present invention, a second command is applied to the memory module via the remainder of the bus during accessing of the memory module, said second command causing lower power consumption in the memory module as compared to said first command.
Preferably, the first command is a write command and the second command is a read command.
Preferably, the memory module has a heat sink associated therewith in addition.
Preferably, the system according to the invention is operated at a clock frequency in the range from approx. 200 MHz.